302 HISTORY OF GEOLOGY AND PALAEONTOLOGY. 



Several geologists, for example Studer and Hoffmann, who 

 agreed with De Beaumont's fundamental ideas of upheaval by 

 volcanic force, and his stratigraphical method of determining 

 the age of mountain-systems, discredited his views regarding 

 the simultaneous upheaval of parallel mountain-chains, as well 

 as his assumption of sudden paroxysmal uplifts. They 

 showed that the Alps, the Harz mountains, and the Erz 

 mountains had suffered from repeated crust-movements. 

 Still others, Constant Prevost, Ami Boue, Conybeare, and 

 Charles Lyell, were in openly avowed opposition to Elie de 

 Beaumont's doctrines from the first. 



Professor Thurmann in Porrentruy made a series of valuable 

 observations on mountain-making processes. This observer, 

 who devoted his life to the study of the Swiss Jura mountains, 

 elucidated their structure and composition with masterly skill 

 and breadth of conception. The arched forms, so conspicuous 

 a feature of the Jura Chain, were explained by Thurmann as 

 crust-uplifts due to vertically-acting subterranean forces, and 

 he quoted several examples to show how these forces may 

 sometimes raise portions of the crust, and sometimes give 

 origin to faults along which the uplifted chains are disjointed, 

 and the several portions move apart. 



Thurmann called the unbroken uplifted chains "arches," 

 and distinguished as " combes " the crust-inthrows faulted into 

 the middle of the arches ; a " combe " wholly surrounded by 

 faults was termed by Thurmann a " cirque." While he used 

 the term "fold" for the crust-arches themselves, he applied 

 that of "val" for the syncline-or trough between neighbouring 

 arches. He also gave distinctive names to mountain-valleys 

 the longitudinal deep ravines at the outer flanks of the chains 

 he termed "ruzs," and the transverse valleys cutting through 

 several chains "cluses." 



The earlier treatises of Thurmann in 1830 and 1836 discuss 

 the orographical features chiefly in relation to the original 

 fold-forms of the Jura system and to general principles of 

 mountain-folding and structures. His complete tectonical 

 results regarding the causes and phenomena of relative crust- 

 displacements were not published until 1856, a year after his 

 death, at the age of fifty-one, from cholera. In these later 

 papers Thurmann recognised the existence of one hundred 

 and sixty incipient chains in the Jura mountains, only thirty 

 of which could be regarded as of primary importance. He 



